DESCRIPTION (Applicant's Description-edited) The pathway of tumor progression and metastasis requires deregulation of multiple genes, including those encoding growth-factors and their membrane receptors. Here the investigator will focus on a novel growth factor associated with metastatic breast cancer and the paraneoplastic syndrome humoral hypercalcemia of malignancy. This factor, designated PTHr12, is a ligand for a G-protein linked transmembrane receptor. Originally discovered by its cross-reactivity with parathyroid hormone (PTH), PTHrp is proposed to function as an autocrine growth factor; its deregulated expression is associated with metastasis to bone and with hypercalcemia. This application focuses on multidimensional NMR studies of the receptor-binding domain of human PTHrp (residues 1-34). The structure of this domain is not only of fundamental interest, but would also provide a basis for design of inhibitors for clinical trials in cancer therapy. Despite its compelling biomedical importance, the crystal structure of PTH-rp is unknown. Previous IH-NMR studies of the receptor-binding domain are of limited resolution, and their interpretation is confounded by use of an organic cosolvent. The investigator's design exploits recent advances in multidimensional NMR technology to test the following propositions: Hypothesis 1) that the receptor- active structure of PTHrp(I-34) contains organized secondary and tertiary structure; and Hypothesis 2) that this receptor-active structure can be deduced by comparative multidimensional NMR study of active and inactive analogs. These hypotheses are supported by a solid foundation of preliminary results that for the first time long-range NOEs are demonstrated in aqueous solution by study of an analog with enhanced receptor-binding potency. The present application offers a combination of novel peptide design and NMR technology to address a central question in the biology of breast cancer.